This might sound a little complicated to anyone who doesn't understand the "Sine Rule" but with a little practice you'll be able to assess the required drift angle by a small amount of mental agility and that your cross-country navigation skills will become easy-peasy.
Firstly, using your CRP-5 (or whatever version you might have) calculate the “Maximum Drift Angle” that you will experience over the leg that you intend to navigate. On a typical UK X-Country flight you’ll not be too far out with the calculation using the maximum wind strength over the entire route. Use this as the basis of “maximum drift” and draw a line on your chart to indicate the generalised wind direction i.e. “maximum drift”. Similarly, calculate your “max groundspeed” with respect to the wind direction… an easy calculation! All of this can be done at the flight planning stage of your route.
At the commencement of your next navigation leg, compare the forecast wind-line to an imaginary line that passes through your longitudinal axis (nose to tail). Using the resultant angle, look at the clock-face of your watch and, if the wind is within 15 degrees of your longitudinal axis (fore or aft), it’s on the “quarter-hour”; therefore, use “1/4” of the “maximum drift angle” (it’s the Sine of 15 degrees i.e. 0.25). If the wind angle is within 30 degrees the Sine value (fore or aft) its 0.5; therefore, use half of the maximum drift value. If the wind angle is within 45 degrees (fore or aft) the Sine value is 0.707; therefore, use ¾ of the maximum drift angle. Beyond 45 degrees… use maximum drift!
Similarly, your groundspeed can easily be assessed in a similar manner. Calculate your maximum groundspeed and indicate this speed against the “max drift” line that you previously drew on your chart. This time… use the Sine of the angle with respect to the angle of the wind from an imaginary line drawn through the wings. If the wind is up to 15 degrees forward from the wing, subtract 1/4 of the wind component from your indicated airspeed; if it’s aft of the wing… add it! If the wind is up to 30 degrees forward of the wing, subtract ½ of the wind component (aft of the wing… add it). If the wind is up to 45 degrees forward of the wing, subtract ¾ of the wind component (aft of the wing… add it). More than 45 degrees forward of the wing, subtract ALL of the wind component (aft of the wing… add it).
Once that you get used to the arithmetical values associated with the wind direction/speed calculation you’ll very quickly be able to recalculate any diversion heading/groundspeed without recourse to the “whizz wheel”.
Complex as this might sound; it forms the very basis of the understanding of pilot navigation and that it takes the fear out of any en-route/diversion calculations that might be faced by a student pilot. Besides which… it will ease your workload by your not having to fumble around with your whizz wheel when that pesky examiner instructs you to divert to XYZ! Establish what you need to do and then… cross check with your whizz wheel when time permits! You’ll be surprised at how accurate your mental calculations can be!
Be safe; fly the aeroplane.
Regards
TCF